1. Field of the Invention
The present invention relates generally to optics and, more specifically, the present invention relates to silicon optical modulators.
2. Background Information
Internet and network data traffic growth pushes toward optical-based data communication. Transmission of multiple optical channels over the same fiber in dense wavelength-division multiplexing (DWDM) systems and Gigabit Ethernet (GBE) systems provides a simple way to use the higher data capacity (signal bandwidth) offered by fiber optics. Commonly used optical components in data communications systems include wavelength division multiplexed (WDM) transmitters and receivers, optical filters such as diffraction gratings, thin-film filters, fiber Bragg gratings, arrayed-waveguide gratings, optical add/drop multiplexers, modulators, lasers and optical switches.
Many of these building block optical components can be implemented in semiconductor devices. In electro-optic switching devices, voltages are applied to selected parts of a device to create electric fields within the device. The electric fields change the optical properties of selected materials within the device and the electro-optic effect results in switching action. Electro-optic devices typically utilize electro-optical materials that combine optical transparency with voltage-variable optical behavior. One typical type of single crystal electro-optical material used in electro-optic switching devices is lithium niobate (LiNbO3). III-V semiconductor compounds such as InP and GaAs have also been used for high-speed modulators.
Silicon photonic integrated circuits offer low cost opto-electronic solutions for applications ranging from telecommunications to chip-to-chip interconnects. An optical modulator is a key component of any optical communications link, however, it is challenging to achieve high speed optical modulation in silicon. Currently, the free carrier plasma dispersion effect is favored for high speed optical modulation in silicon. In this approach, a change in free carrier density in a silicon waveguide results in a change in the refractive index of the material. The refractive index change modifies the optical phase of light passing through it. The speed at which this modulation can be done is limited in part by how fast the free carriers can be injected into or removed from the waveguide, the region occupied by the traveling optical mode.